1. Field of the Invention
The present invention relates to a voltage regulator that is disposed as a power source of a portable apparatus or an electronic apparatus so as to output a constant voltage, and more particularly, to a voltage regulator that can suppress an occurrence of overshooting in an output voltage at the time of starting a power source with a source voltage.
2. Background Art
A voltage regulator according to the related art will be described below. FIG. 3 is a circuit diagram illustrating a voltage regulator according to the related art.
The voltage regulator according to the related art includes an error amplifier circuit 104, a reference voltage circuit 103, PMOS transistors 901 and 902, an output transistor 110, resistors 105 and 106, and 903, a capacitor 904, a ground terminal 100, an output terminal 102, and a power source terminal 101.
The resistors 105 and 106 are disposed in series between the output terminal 102 and the ground terminal 100 and divide an output voltage Vout of the output terminal 102. When the voltage of the connecting point of the resistors 105 and 106 is defined as Vfb, the error amplifier circuit 104 controls the gate voltage of the output transistor 110 such that the voltage Vfb gets close to the voltage Vref of the reference voltage circuit 103, and outputs the output voltage Vout to the output terminal 102. When the source voltage VDD of the power source terminal 101 increases, a current Ix1 flows from the power source terminal 101 to the fluctuation detecting capacitor 904. The current Ix1 is amplified by a current feedback circuit including the PMOS transistors 901 and 902 and the resistor 903 and a current Ix2 is generated. The current Ix2 is supplied to the gate of the output transistor 110 and charges the gate capacitor of the output transistor 110. In this way, the gate-source voltage VGS of the output transistor 110 is regulated to an appropriate value even when the source voltage VDD fluctuates and it is thus possible to suppress the overshooting and to stabilize the output voltage (for example, see Patent Document 1).
[Patent Document 1] Japanese Patent Application Laid-Open No. 2007-157071